Letter from Stephanie: Temperature & Albedo

Dear Fellow Explorers,

Antarctica holds the world record for the coldest temperatures. Vostok Station hit -89.5ºC (-129ºF). The South Pole commonly boasts temperatures in the low 50's.... that's 50ºC BELOW freezing. But it's not always that cold–just last week we had a balmy -15ºC day!

When faced with a trip to Antarctica, what clothing do I pack? I usually throw some long underwear, jeans, socks, a few turtlenecks, tennis shoes, and a favorite sweater or two into a duffel bag. Oh–and I pack lots and lots of hand lotion. And then I head south.

What? No coat?! Well, after all, I work in the warmer parts of Antarctica–where the temperature hovers around -10ºC or so during balmy summer months of January and February.

Still not satisfied? You're right, I do need a coat, but I don't bring my own. Before flying to Antarctica, I stop in New Zealand to get outfitted by the polar service contractor of the National Science Foundation. To ensure that researchers have the right gear, polar service contractors provide everyone who lives and works in Antarctica with all outer clothing layers. They want to make sure everyone is prepared for the weather adequately–safety is the primary concern. I get bunny boots, wind pants, pants and a coat made of polar fleece, some flannel shirts, a few extra pairs of thermal underwear, many pairs of gloves, a set of goggles.... and a big, red, warm, polar parka.

The temperatures actually vary quite a bit around Antarctica. Temperatures along the coast are warm because the ocean warms the air–this is where I work. The Antarctic Peninsula is actually the warmest Antarctic region. Mean (average) annual coastal temperatures are -17ºC (-1ºF); the summer average hovers at freezing. I've actually worked in the rain at Palmer Station; temperatures there can get as high as 9ºC (48ºF) in the summer. The winter temperatures average -20º to -30ºC (-4º to -22ºF), but can get as low as -50ºC (-58ºF)!

Though temperatures can vary a lot between seasons, they don't change much each day. That's because the light patterns don't change much each day. If the Sun is shining all the time, as it does in summer, temperatures don't drop drastically. It's the same in winter, when it's always dark; without sunlight, temperatures can't rise much! Polar regions like Antarctica have small diurnal (daily) changes.

Why is Antarctica the coldest place on Earth? Well, there are three main reasons.

First, Earth is a sphere. Light and heat from the Sun strike the surface at the Equator straight-on, but the polar regions, where the Earth curves most, get that same light and heat at an angle. In other words, because of the curve of the Earth's surface, light hitting the North and South polar regions spreads across a larger area; this energy strikes the surface at a lower angle. The North and South poles only get about 60% of light and warmth that reaches the Equator! On the other hand, the poles at least get more light and warmth than any other location on the globe during the summer. (Why then doesn't it get warmer there? Investigate the next reason!)

Another reason for Antarctica's extremely cold temperatures is its high albedo, the amount of solar radiation reflected from a surface. Antarctica is covered with snow and ice; the ice surface is very reflective. Most of the sunlight hitting Antarctica is reflected right back out; very little radiation, or heat, is absorbed into the surface.

Albedo = 0; no radiation is reflected and all is absorbed. Albedo = 100; all radiation is reflected.

Ocean surfaces usually are dark; they have an albedo of about 10-15%. The Antarctic ice sheets, which are white, act like a mirror; the surface albedo can be as high as 90%!

The final reason Antarctica is so cold? The clear atmosphere! Antarctica is far away from all of our cars and factories and even our lit-up cities. There are few particles of dust or pollution, or water vapor to trap and scatter reflected radiation–radiation that would warm the polar areas. This clarity of atmosphere is one of the reasons so many astronomers work in Antarctica–they have a clear view of outer space!

Radiation (or heat) absorbed by Earth's surfaces on different parts of the globe.

Besides being very cold, Antarctica is also very dry. You might imagine that it is always snowing in Antarctica, but it actually snows very little. However, because the snow doesn't melt, it builds up year to year. Antarctica is actually a polar desert! The South Pole gets less than an inch of snow each year! The continent receives an average of less than one meter (3 feet) of precipitation each year. Most snow falls within 200 to 300 kilometers (120 to 190 miles) of the coast because the big storm systems can only carry the snow that far. The Antarctic Peninsula has the highest precipitation of the continent, 90 centimeters (36 inches). This is why I take so much hand lotion with me when I come to Antarctica. Not only does it rarely rain or snow, but the air there hardly holds moisture; cold air carries less moisture than warm air. Relative humidity in Antarctica can be as low as 1%! For comparison, the relative humidity of a "dry" winter day in the Northeastern United States is typically 20-25%.

Keeping track of how much snow falls is very frustrating. Winds and blizzards blow the snow into and out of precipitation gauges, making it difficult to figure out how much new snow fell.

Well, it's time to get back to work. I'm about to head out onto the deck to help collect a sample of sediment from the ocean floor–but first, I had better put on all of my layers. Once I'm finished dressing to go outside, I look kind of like a little kid in a snowsuit–I get to stay nice and warm, but with so many layers, I can barely move!